Operating a sub-sea organic Rankine cycle (ORC) system using individual pressure vessels

ABSTRACT

A method and system for generating electrical power for sub-sea applications includes assembling each of the main components ( 132, 138, 142, 146 ) of an organic Rankine cycle (ORC) system ( 100 ) inside a pressure vessel to form a series of vessels ( 104, 106, 108, 110 ) removably connected to one another and configured to be placed near, on or below a sea floor. The main components of the ORC system include an evaporator ( 132 ), a turbine ( 138 ), a condenser ( 142 ) and a pump ( 146 ). A working fluid ( 135 ) is circulated through the pressure vessels in order to generate mechanical shaft power that is converted to electrical power (P). In some embodiments, the ORC system includes at least one redundant component that corresponds to one of the main components. The working fluid may be circulated through at least one redundant ORC component such that the ORC system is able to continue operating when one of more of the main components is not operating properly. A control system ( 148 ) is used to monitor operation of the main components and at least one redundant ORC component. In some embodiments, at least one redundant ORC component is housed in a pressure vessel with its corresponding main component. In other embodiments, at least one redundant ORC component is housed in a separate pressure vessel.

BACKGROUND

The present disclosure relates to an organic Rankine cycle (ORC) system.More particularly, the present disclosure relates to using an ORC systemfor sub-sea applications, whereby the main components of the ORC systemare housed in separate pressure vessels.

In downhole oil and gas wells, electrical power may be required forvarious pieces of equipment and accessories, such as well telemetryequipment, well logging equipment, sensors, telecommunication devices,and equipment for pumping oil to the surface oil rig. Electrical powermay be supplied from the surface (i.e. from the oil rig); however, thisrequires electrical wiring to span large distances. Alternatively, fuelcells and/or batteries may also be used as power sources in sub-seaapplications.

Rankine cycle systems are commonly used for generating electrical power,and have been used in sub-sea applications. However, the sub-seaoperating environment requires large and expensive equipment. There is aneed for an improved method and system of producing electrical power forsub-sea applications.

SUMMARY

A method and system is described herein for generating electrical powerfor sub-sea applications using an organic Rankine cycle (ORC) systemhaving an evaporator, a turbine, a condenser and a pump, which aredefined as main components of the ORC system. The method comprisesassembling each of the main components inside a separate pressure vesselto form a series of vessels removably connected to one another andconfigured to be placed near, on or below a sea floor. A working fluidis circulated through the pressure vessels in order to generatemechanical shaft power that is converted to electrical power.

In some embodiments, the ORC system includes at least one redundant ORCcomponent selected from a group consisting of a second evaporator, asecond turbine, a second condenser and a second pump. The working fluidmay be circulated through at least one redundant ORC component such thatthe ORC system is able to continue operating when one or more of themain components is not operating properly. A control system is used tomonitor operation of the evaporator, the turbine, the condenser, thepump and at least one redundant ORC component. In some embodiments, atleast one redundant ORC component is housed in a pressure vessel with acorresponding main component. In other embodiments, at least oneredundant ORC component is housed in a separate pressure vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an organic Rankine cycle (ORC) systemdesigned to produce electrical power using waste heat.

FIG. 2 is a schematic of an ORC system installed on a sea floor. Each ofthe main components of the ORC system is housed in a separate pressurevessel.

FIG. 3 is a block diagram of the ORC system of FIG. 2.

FIG. 4 is a block diagram of an alternative embodiment of the ORC systemof FIG. 3. Each of the main components of the ORC system includes aredundant component and a sub-controller.

FIG. 5 is an exploded view of the condenser pressure vessel from FIG. 4,as an example, to further illustrate operation of the main condenser andthe redundant condenser, as controlled by the sub-controller.

FIG. 5A is an alternative embodiment of the condenser pressure vessel ofFIG. 5 and includes an intermediary heat exchanger and cooling fluid.

FIG. 6 is a flow diagram of a method of operating the condenser pressurevessel of FIG. 5.

FIG. 7 is a block diagram of another alternative embodiment of an ORCsystem having redundant components, whereby some of the redundantcomponents are housed in separate pressure vessels.

It is noted that the figures are not to scale.

DETAILED DESCRIPTION

A Rankine cycle system may be used to generate electrical power that isused for operation of downhole oil and gas wells. The Rankine cyclesystem uses waste heat and a working fluid (i.e. water) to drive agenerator that produces electrical power. An organic Rankine cycle (ORC)system operates similarly to a traditional Rankine cycle, except that anorganic Rankine cycle (ORC) system uses an organic fluid, instead ofwater, as the working fluid. Because some of the organic working fluidsvaporize at a lower temperature than water, a lower temperature wasteheat source may be used in an ORC system.

To optimize efficiency in sub-sea applications, the ORC system ispreferably placed on or near the sea floor so that it is relativelyclose to where the electrical power is to be supplied. As describedbelow, unique challenges exist in sub-sea operation of an ORC system.The system and method described herein includes an ORC system in whicheach of the main components of the ORC system is housed in a separatepressure vessel. In some embodiments, the main components of the ORCsystem have corresponding redundant components, which may be used inparallel with the main component or in place of the main component.

FIG. 1 is a schematic of a traditional ORC system 10, which includescondenser 12, pump 14, evaporator 16, and turbine 18. Organic workingfluid 22 circulates through system 10 and is used to generate electricalpower. Liquid working fluid 22 a from condenser 12 passes through pump14, resulting in an increase in pressure. High pressure liquid fluid 22a enters evaporator 16, which utilizes heat source 24 to vaporize fluid22. Heat source 24 may include, but is not limited to, any type of wasteheat resource, including reciprocating engines, fuel cells, andmicroturbines, and other types of heat sources such as solar, geothermalor waste gas. Working fluid 22 exits evaporator 16 as a vapor (22 b), atwhich point it passes into turbine 18. Vaporized working fluid 22 b isused to drive turbine 18, which in turn powers generator 28 such thatgenerator 28 produces electrical power. Vaporized working fluid 22 bexiting turbine 18 is returned to condenser 12, where it is condensedback to liquid 22 a. Heat sink 30 is used to provide cooling tocondenser 12.

For sub-sea applications in which the electrical power from ORC system10 is used for oil well equipment, heat source 24 may be a sub-seageothermal source (for example, oil being removed from an oil well). Forpurposes of this disclosure, oil refers to oil or an oil and watermixture. In preferred embodiments, ORC system 10 uses the samegeothermal source that is being extracted by the drilling equipment. Inan alternative embodiment, a dedicated geothermal source may be used bythe ORC system. Heat sink 30 may be the surrounding cold sea water. Atthe sea depths for oil drilling applications, the water temperature isapproximately 39 degrees Fahrenheit (approximately 4 degrees Celsius).

Given the availability of a heat source and a heat sink, ORC system 10is well-suited for producing electrical power for operation of the oilwell and other equipment. An ORC system like system 10 of FIG. 1 wouldgenerally have all of its main components contained within a singlepressure vessel. In some cases, condenser 12 may be contained outside ofthe pressure vessel. In either case, the pressure vessel would have tobe large enough to contain all of the components of system 10, as shownin FIG. 1, with the possible exception of condenser 12. The pressurevessel would be located on or just above the sea floor; alternatively,the pressure vessel could be located below the sea floor. In any case,the pressure vessel is subject to large pressures and consequently mustbe built accordingly.

This makes the housing for ORC system 10 expensive. Moreover,accessibility to the components inside the pressure vessel is limitedand requires shut-down of system 10.

FIG. 2 is a schematic of ORC system 100 located on sea floor 102 of sea101 and including first pressure vessel 104, second pressure vessel 106,third pressure vessel 108, fourth pressure vessel 110, and fifthpressure vessel 112. First pressure vessel 104 houses an evaporator andis removably connected to second pressure vessel 106 through pipingsegment 114. Second pressure vessel 106 is also removably connected tothird pressure vessel 108 through piping segment 116, and houses aturbine. Similarly, third pressure vessel 108 is removably connected tofourth pressure vessel 110 by piping segment 118. A condenser iscontained within vessel 108. Forth pressure vessel 110 houses a pump andis removably connected to third pressure vessel 108 and first pressurevessel 104. Piping segment 120 connects fourth pressure vessel 110 tofirst pressure vessel 104. First, second, third and fourth pressurevessels 104, 106, 108 and 110 are removably connected to one another viapiping segments 114, 116, 118 and 120 such that a working fluid is ableto circulate through ORC system 100, as described above in reference toFIG. 1.

Fifth pressure vessel 112 contains a control system for controllingoperation of ORC system 100, and is discussed further below.

As illustrated in FIG. 2, first pressure vessel 104 is also removablyconnected to oil well casing 122 by piping segments 124 and 126. Oilwell casing 122 is used to deliver oil from an oil well to a surface oilrig (not shown). A mixture of oil and hot water passes through wellcasing 122; the geothermal mixture is at a temperature ranging betweenapproximately 200 and 350 degrees Fahrenheit (93 and 177 degreesCelsius). This geothermal mixture of oil and water is used as a heatsource for the evaporator in pressure vessel 104. In the exemplaryembodiment shown in FIG. 2, a portion of the oil passing through wellcasing 122 is bypassed into piping segment 124, where it is thendirected through the evaporator in pressure vessel 104. The oil thentravels back to well casing 122 through piping segment 126. In thisembodiment, ORC system 100 is able to use a geothermal source alreadybeing extracted. In an alternative embodiment, the ORC system may haveits own dedicated oil well to extract oil used strictly as a heat sourcefor the evaporator of the ORC system.

As stated above, the geothermal source from the oil well is commonly amixture of oil and water. In some cases, it may be a two phase mixtureof oil, water and gas. In some embodiments, the sub-sea geothermalsource may be essentially all hot water and essentially no oil. In otherembodiments, the sub-sea geothermal source may be a water and gasmixture.

The condenser of ORC system 100, which is housed in pressure vessel 108,may be a water-cooled condenser. Piping segments 128 and 129 may beremovably connected to third pressure vessel 108. Piping segment 128 isopen on one end and pump 130 is configured to pump cold sea water 131through piping 128 and into pressure vessel 108. Depending in part on adepth of sea 101, sea water 131 near sea floor 102 may be at atemperature ranging between approximately 32 and 72 degrees Fahrenheit(zero and 22 degrees Celsius). At depths greater than approximately 1000meters (1094 yards), the water temperature is typically less than about40 degrees Fahrenheit (about 5 degrees Celsius). As such, cold sea water131 is well suited as a heat sink for the condenser inside pressurevessel 108. After passing through the condenser, sea water 131 isrecycled back into sea 101 through piping 129.

Piping segments 114, 116, 118, 120, 124, 126, 128 and 129 may be, forexample, stainless steel piping which is attached to pressure vessels104, 106, 108 and 110 through traditional welding techniques. Otherknown fittings may also be used, particularly those well suited forunderwater applications. In preferred embodiments, quick connectfittings are used so that pressure vessels 104, 106, 108 and 110 may beeasily disconnected from ORC system 100 and other pressure vessels maybe added into system 100.

As shown in FIG. 2, pressure vessel 112, which contains a controlsystem, has wired connection to pressure vessels 104, 106, 108 and 110via wires 115. Wires 115 may be configured to provide an electricalconnection or an optical connection between the control system insidepressure vessel 112 and the ORC components inside pressure vessels 104,106, 108 and 110. In an alternative embodiment, sonar transmission couldbe used for communicating between the control system and the ORCcomponents. In yet another embodiment, some of the electrical wiresconnecting the controller of vessel 112 to the ORC components could becontained with piping segments 114, 116, 118 and 120. Each of the ORCcomponents of ORC system 100 requires electrical power for operation. Assuch, wires may be used to deliver electrical power to the ORCcomponents. In an alternative embodiment, the electrical power linescould also be used as communication lines between the control system andthe ORC components.

In the exemplary embodiment shown in FIG. 2, the pressure vessels of ORCsystem 100 are placed directly on sea floor 102. The pressure vesselsmay alternatively be elevated slightly above sea floor 102. For example,some or all of the pressure vessels may be on stilts or on a platform.Moreover, some or all of the pressure vessels may be placed below seafloor 102. Various configurations are possible; however, it is preferredthat the pressure vessels of ORC system 100 are located close to thegeothermal heat source (i.e. oil) to be used by the evaporator. Inaddition, ORC system 100 should be located close to the equipmentintended to receive the electrical power produced by ORC system 100.

FIG. 3 is a block diagram of ORC system 100 of FIG. 2 and includesfirst, second, third, fourth and fifth pressure vessels 104, 106, 108,110, and 112. Evaporator 132 is contained within first pressure vessel104. As similarly described above in reference to ORC system 10 of FIG.1, organic working fluid 135 enters first pressure vessel 104 as a highpressure liquid 135 a and passes through evaporator 132. Sub-seageothermal heat source 136 (from well casing 122 of FIG. 2) also passesthrough evaporator 132 and vaporizes working fluid 135. Vaporizedworking fluid 135 b exits pressure vessel 104 and passes through tosecond pressure vessel 106, which contains turbine 138 and generator140. Vaporized working fluid 135 b expands to drive turbine 138, whichproduces mechanical shaft energy. Turbine 138 is coupled to generator140 such that the mechanical shaft energy from turbine 138 is convertedto electrical power P. Vaporized working fluid 135 b exits secondpressure vessel 106 and passes through to third pressure vessel 108 andcondenser 142 housed inside vessel 108. Sea water 131 is pumped out ofsea 101 and enters vessel 108 such that it circulates through condenser142 and functions as a heat sink to condense working fluid 135 back toliquid 135 a. Pump 146 is contained within fourth pressure vessel 110and is used to increase a pressure of liquid working fluid 135 a, whichis then recycled back to first pressure vessel 104 and evaporator 132.

Evaporator 132, turbine 138, condenser 142 and pump 146 are the maincomponents of ORC system 100. Controller 148 contained within fifthpressure vessel 112 controls operation of each of the main components ofORC system 100. Sensors are used to sense various parameters of each ofthe main components and relay the sensed parameters to controller 148.This is described in further detail below in reference to FIG. 5.Controller 148 thus monitors whether the components of ORC system 100are operating properly.

In the exemplary embodiment shown in FIG. 3, ORC system 100 includespower conditioner 150, which is housed inside sixth pressure vessel 152.Power conditioner 150 is not an essential component of ORC system 100,but is included in preferred embodiments. Electrical power P generatedinside second pressure vessel 106 passes into pressure vessel 152 and topower conditioner 150, where electrical power P is conditioned to anappropriate voltage for direct current (DC), or an appropriate voltage,frequency, phase and power factor for alternating current (AC).Conditioned electrical power P′ may then be distributed to sub-sea wellequipment as needed. During times in which power is not being demandedby the sub-sea well equipment, conditioned electrical power P′ may bedistributed to resistive bank 154, which may act as an artificial loadfor ORC system 100. Resistive bank 154 may use cold sea water forcooling, similar to condenser 142. Controller 148 may also monitor andcontrol operation of power conditioner 150 and resistive bank 154.

As shown in FIG. 3, turbine 138 and generator 140 are housed within asingle pressure vessel (i.e. vessel 106). In other embodiments, turbine138 and generator 140 may be in separate pressure vessels connected toone another. However, for efficiency purposes, it is preferred thatturbine 138 and generator 140 are housed in a single pressure vessel.Power conditioner 150 is shown inside pressure vessel 152 and electricalpower P passes from second pressure vessel 106 to pressure vessel 152.In alternative embodiments, power conditioner 150 may be housed in thesame pressure vessel as generator 140 (i.e. pressure vessel 106).

ORC system 100 utilizes sub-sea geothermal source 136 (i.e. oil oroil/water mixture) as a heat source and sea water 131 as a heat sink. Asdescribed above, oil 136 from well casing 122 passes directly throughevaporator 132 to vaporize working fluid 135. In an alternativeembodiment, a heat exchanger (not shown) may be housed inside pressurevessel 104. Oil 136 may pass through the heat exchanger, instead ofevaporator 132, and transfer heat to an intermediary fluid, which thenpasses through evaporator 132. Similarly, third pressure vessel 108 mayalso contain a heat exchanger (not shown). Instead of passing directlythrough condenser 142, sea water 131 may pass through the heat exchangerand receive heat from an intermediary fluid, which then passes throughcondenser 142. (See FIG. 5A.) Heat exchangers may be used in pressurevessels 104 and/or 106 to avoid any issues with using oil and sea water(salt water) inside evaporator 132 and condenser 142.

In the exemplary embodiment shown in FIG. 3, each of the main componentsof ORC system 100 is controlled by controller 148. In an alternativeembodiment, some or all of the components may have a sub-controllerwhich communicates with main controller 148. In that case, thesub-controller would generally be housed within the pressure vesselcontaining the ORC component.

By housing the main components of ORC system 100 in separate pressurevessels, as opposed to having the ORC system contained within a singlepressure vessel, some of the challenges in designing a sub-sea ORCsystem are eliminated in the embodiment shown in FIGS. 2 and 3. Oil istypically extracted in areas where the sea water is deep, thus resultingin a high pressure environment at and near the sea floor. Therefore, apressure vessel for containing an ORC system is designed with thickexternal walls. If all of the ORC components are to be contained withinone pressure vessel, the pressure vessel would have a large diameter. Asthe diameter of the pressure vessel increases, the thickness of theexternal wall of the pressure vessel increases significantly, making theORC system expensive. Having separate pressure vessels for eachcomponent of the ORC system allows the pressure vessels to be smaller insize and wall thickness, which may reduce material costs. Moreover, thesmaller pressure vessels are easier to handle, particularly duringinstallation. ORC system 100 is designed such that pressure vessels 104,106, 108, 110 and 112 are removably connected to one another. From aserviceability standpoint, this allows another pressure vessel to besubstituted for a pressure vessel that contains a malfunctioningcomponent. Thus, system 100 provides greater flexibility for swappingout components.

FIG. 4 is a block diagram representing another embodiment of an ORCsystem. ORC system 200 is similar to ORC system 100, and like referenceelements are designated with the same number, except in FIG. 4 thenumbers start with a “2” instead of a “1”. (For example, working fluid135 in ORC system 100 of FIG. 3 is designated as 235 in ORC system 200of FIG. 4.) A main difference between ORC system 100 of FIG. 3 and ORCsystem 200 of FIG. 4 is the pressure vessels for the main components ofORC system 200 also include a redundant component designed to operate inparallel with the main component or in place of the main component.

ORC system 200 includes first pressure vessel 204, second pressurevessel 206, third pressure vessel 208, fourth pressure vessel 210, fifthpressure vessel 212 and sixth pressure vessel 252. As described above inreference to FIG. 3, ORC system 200 uses geothermal heat source 236 forheating and sea water 231 for cooling. Working fluid 235 circulatesthrough ORC system 200. Fifth pressure vessel 212 houses main controller248. In ORC system 200, a cascaded control system is used in which maincontroller 248 is connected to sub-controllers, as described below.

First pressure vessel 204 includes first evaporator 232, secondevaporator 233 and first sub-controller 256. First evaporator 232 isdefined as a main component of ORC system 200 and functions as the mainevaporator of ORC system 200. Second evaporator 233 is defined as aredundant component or a redundant evaporator of ORC system 200.Pressure vessel 204 is configured such that working fluid 235 entersvessel 204 as liquid 235 a and may flow through first evaporator 232and/or second evaporator 233. Geothermal heat source 236 also enterspressure vessel 204. Although not shown in FIG. 4, geothermal heatsource 236 may also pass through first evaporator 232 and/or secondevaporator 233. First sub-controller 256 is configured to controlwhether heat source 236 and working fluid 235 pass through both or onlyone of evaporators 232 and 233. Sensors (not shown) may be used at aninlet and/or an outlet of evaporators 232 and 233 and relay sensedparameters to controller 256. Based on data from the sensors, controller256 controls flow through evaporators 232 and 233 by using valves (notshown) at an inlet and/or an outlet of evaporators 232 and 233. (SeeFIGS. 5 and 6 and the description below for more detail on regulatingflow through main evaporator 232 and redundant evaporator 233.)

Second pressure vessel 206 includes first turbine 238, second turbine239, first generator 240, second generator 241 and second sub-controller258. First turbine 238 and first generator 240 are defined as the mainturbine and generator of ORC system 200. Second turbine 239 and secondgenerator 241 are defined as the redundant turbine and generator of ORCsystem 200. First and second turbines 238 and 239 are configured toreceive vaporized working fluid 235 b passing from pressure vessel 204,and generate mechanical shaft energy convertible to electrical power Pin first and second generators 240 and 241. Electrical power P fromfirst and second generators 240 and 241 flows to sixth pressure vessel252. Working fluid 235 b exiting turbines 238 and 239 flows frompressure vessel 206 to pressure vessel 208.

Sixth pressure vessel 252 contains first power conditioner 250, secondpower conditioner 251 and sub-controller 260. Power conditioner 250 maybe the main power conditioner and power conditioner 251 may be used as aredundant component or as a substitute if sub-controller 260 determinesthat there are problems with power conditioner 250. Conditioned power P′exits pressure vessel 252 and may then be delivered to the sub-sea wellequipment.

A resistive bank has been removed from FIG. 4 for clarity; however, itis recognized that a resistive bank, similar to resistive bank 154 ofFIG. 3, may be used during times when there is no electrical load or aminimal electrical load. In ORC system 200, the resistive bank may becontrolled by main controller 248 or by sub-controller 260 insidepressure vessel 252. Alternatively, the resistive bank may have its ownsub-controller connected to main controller 248.

Third pressure vessel 208 contains first condenser 242, second condenser243 and sub-controller 262. First condenser 242 may be defined as a maincomponent and second condenser 243 may be defined as a redundantcomponent. Similar to pressure vessel 204 housing evaporators 232 and233, pressure vessel 208 includes two inlet and two outlet streams. Afirst inlet stream is working fluid 135 b, which may pass through firstcondenser 242 and/or second condenser 243. Vaporized working fluid 135 bis condensed to liquid working fluid 135 a which then passes through anoutlet of pressure vessel 208 and travels to fourth pressure vessel 210.The second inlet stream is sea water 231, which acts as a heat sink.Cold sea water 231 enters pressure vessel 208 and passes through atleast one of first condenser 242 and second condenser 243. Sea water 231then exits pressure vessel 208 and is recycled back into the sea.

Working fluid 135 b passes through at least one of first condenser 242and second condenser 243. Valves (not shown in FIG. 4) at an inletand/or an outlet of condensers 242 and 243 may be used to permit orsuppress flow through condensers 242 and 243. Sub-controller 262controls operation of the valves. This is described in further detailbelow in reference to FIGS. 5 and 6.

Fourth pressure vessel 210 includes first pump 246, second pump 247 andsub-controller 264. First pump 246 may be defined as a main component;and second pump 247 may be defined as a redundant component. Liquidworking fluid 235 a enters pressure vessel 210 and flows through firstpump 246 and/or second pump 247. Sub-controller 264 controls flowthrough first and second pumps 246 and 247 using valves (not shown) andbased upon sensed parameters inside pressure vessel 210.

FIG. 5 is an exploded view of third pressure vessel 208 from FIG. 4 andheat sink 231 (cold sea water) to better illustrate the inlet and outletstreams of pressure vessel 208, and control of first and secondcondensers 242 and 243 by sub-controller 262. As explained above,vaporized working fluid 235 b from second pressure vessel 206 flows intopressure vessel 208, which is designed such that fluid 235 b may thenflow through first condenser 242 and/or second condenser 243. Similarly,inlet stream 231 a of cold sea water 231 enters pressure vessel 208 andmay then flow through first condenser 242 and/or second condenser 243.Cold sea water 231 is used to condense vaporized fluid 235 b such thatfluid 235 condenses to liquid 235 a. Outlet streams 231 b fromcondensers 242 and 243 have absorbed heat from fluid 235. Streams 231 bthen exit pressure vessel 208 and are recycled back into the sea. In theembodiment of FIG. 5, two sea water outlet streams 231 b are shownexiting vessel 208. It is recognized that sea water outlet streams 231 bmay be combined at some junction inside pressure vessel 208 such thatone outlet stream 231 b exits vessel 208.

Sub-controller 262 controls flow of vaporized working fluid 235 b andsea water 231 through first and second condensers 242 and 243.Sub-controller 262 may split flow evenly through condensers 242 and 243.Alternatively, controller 262 may direct all flow through firstcondenser 242, unless condenser 242 is malfunctioning. This is describedin further detail below in reference to FIG. 6.

To monitor and control operation of first and second condensers 242 and243, controller 262 uses sensors at various locations inside pressurevessel 208. Sensor 268 is placed in sea water inlet stream 231 a forfirst condenser 242. Sensor 270 is placed in inlet stream 231 a forsecond condenser 243. Sensors 268 and 270 may sense temperatures andpressures of inlet stream 231 a, which is then relayed to sub-controller262. Similarly, sensors 272 and 274 are placed in inlet streams forworking fluid 235 b entering first and second condensers 242 and 243.Sensors 272 and 274 may also sense temperatures and pressures of workingfluid 235 b entering condensers 242 and 243, and the data is conveyed tosub-controller 262.

In the embodiment shown in FIG. 5, the inlet stream of working fluid 235b for condenser 242 and the inlet stream of working fluid 235 b forcondenser 243 each have a sensor. In an alternative embodiment, onesensor may be placed in the stream for working fluid 235 b prior to thepoint at which working fluid 235 b splits into two inlet streams.Similarly, sensors 276 and 278 are placed in each of two sea water inletsteams 231 a entering first condenser 242 and second condenser 243.Because the two sea water inlet streams are the same, it is recognizedthat one sensor may be used.

Sensor 276 is shown in sea water outlet stream 231 b from firstcondenser 242. Sensor 278 is similarly located in outlet stream 231 bfrom second condenser 243. In this case, sensors dedicated to eachcondenser 242 and 243 are necessary for outlet stream 231 b in order toseparately monitor operation of condensers 242 and 243. Similarly,sensor 280 is located in an outlet stream of working fluid 235 a fromfirst condenser 242, and sensor 282 is located in an outlet stream ofworking fluid 235 a from second condenser 243. Again, separate sensorsare needed to monitor working fluid 235 a exiting each condenser andevaluate individual performance of condensers 242 and 243. Parameterssensed by sensors 276, 278, 280 and 282 may include, but are not limitedto, temperature and pressure.

As shown in FIG. 5, valve 284 is installed in the outlet stream ofworking fluid 235 a from condenser 242; valve 286 is installed in theworking fluid outlet stream from condenser 243. Operation of valves 284and 286 is controlled by sub-controller 262. If valve 284 is closed,condenser 242 eventually becomes filled with working fluid 235 andadditional working fluid 235 b entering pressure vessel 208 is no longerable to enter first condenser 242. In that case, so long as valve 286 ofsecond condenser 243 is open, all of working fluid 235 b enteringpressure vessel 208 is directed through second condenser 243.

In an alternative embodiment, valves 284 and 286 may instead be placedin the inlet streams of working fluid 235; or valves may be used in boththe inlet and the outlet streams.

In the embodiment illustrated in FIG. 5, there are no valves installedin the inlet or the outlet of sea water streams 231 a and 231 b. Becausethere is essentially an unlimited amount of sea water 231 to function asa heat sink for condensers 242 and 243, it is not critical that the flowof sea water through condensers 242 and 243 be controlled. However, itis recognized that valves may be used at either an inlet or an outlet ofcondensers 242 and 243 to control flow of sea water 231 throughcondensers 242 and 243.

Pressure vessel 208 is used as an example in FIG. 5 to illustrate anddescribe use of sensors, valves and sub-controller 262 with condensers242 and 243. The other pressure vessels, particularly first pressurevessel 204, second pressure vessel 206 and fifth pressure vessel 210,are similarly designed with sensors and valves. The sensors aresimilarly used in the other pressure vessels to sense temperatures andpressures of working fluid 235 at an inlet and an outlet of thecomponents.

Referring to FIG. 4, pressure vessel 206 contains first turbine 238 andfirst generator 240, as well as second turbine 239 and second generator241. Sensors may be placed in the inlet and the outlet stream forworking fluid 235 flowing through first turbine 238 and second turbine239. Again, temperatures and pressures are sensed and relayed tosub-controller 258. Sensors also may be placed at an inlet and an outletof first generator 240 and second generator 241 to monitor operation ofgenerators 240 and 241. To analyze whether generators 240 and 241 areoperating properly, sensed parameters may include voltage and current.

Referring back to FIG. 5, in this embodiment, sea water 231 flowsdirectly through condensers 242 and 243. In an exemplary embodiment inwhich condensers 242 and 243 are tube and shell type heat exchangers, itis preferred that sea water 231 runs inside the tubes, rather than onthe shell side of the heat exchanger. The tubes of the heat exchangerare better able to handle high pressures of sea water 231.

Given the corrosiveness of the salt in sea water 231, it may bepreferred, in some cases, to use an intermediary fluid as the coolingfluid in condensers 242 and 243. FIG. 5A is an alternative embodiment topressure vessel 208 of FIG. 5. In the embodiment shown in FIG. 5A,pressure vessel 308 includes intermediary heat exchanger 310 and coolingfluid 312. Instead of flowing sea water 231 through condenser 242 and/orcondenser 243, sea water 231 flows through intermediary heat exchanger310 and receives heat from cooling fluid 312, also flowing through heatexchanger 310. Cooling fluid 312 thus exits heat exchanger 310 at alower temperature compared to its inlet temperature. Cooling fluid 312then enters first condenser 242 and/or second condenser 243 as fluid 312a and receives heat from working fluid 235 passing through condenser 242and/or condenser 243. Cooling fluid 312 exits condenser 242 and/orcondenser 243 as fluid 312 b and circulates back through heat exchanger310.

As shown in FIG. 5A, sensors are used at the same input and outputlocations of condensers 242 and 243. Sensors 368 and 370 are installedin cooling fluid inlet streams 312 a for condensers 242 and 243. Sensors376 and 378 are installed in cooling fluid outlet streams 312 b. Inorder to monitor operation of heat exchanger 310, sensor 388 may beinstalled in sea inlet stream 231 a at an inlet side of heat exchanger310, and sensor 390 may be installed in sea stream 231 b at an outletside of heat exchanger 310. Sensors 388 and 390 relay sensed parametersto sub-controller 262. Although not shown in FIG. 5A, valves may be usedto control flow of cooling fluid 312 through condenser 242 and condenser243.

Referring to FIG. 4 and first pressure vessel 204, geothermal heatsource 236 is described above as passing directly through evaporator 232and evaporator 233. In an alternative embodiment, vessel 204 may containan intermediary heat exchanger, similar to heat exchanger 310 of FIG.5A, which is used to transfer heat from geothermal heat source 236 to anintermediary fluid. The intermediary fluid then passes throughevaporators 232 and 233 to vaporize working fluid 235.

FIG. 6 is a flow diagram illustrating method 400 for operating pressurevessel 208 of FIG. 5. Method 400 includes steps 402-422, and begins withanalyzing the status of first condenser 242 and second condenser 243(step 402) as a function of input from sensors 268, 270, 272, 274, 276,278, 280 and 282. Step 402 is performed by sub-controller 262. Based onsensed parameters and a comparison among the sensed parameters,sub-controller 262 is able to conclude whether condensers 242 and 243are operating properly. For example, based on a comparison of the inlettemperature and pressure of working fluid 235 (determined by sensor 272)and the outlet temperature and pressure of fluid 235 (determined bysensor 280), controller 262 analyzes whether condenser 242 is operatingproperly. Controller 262 may also use the temperature and pressure datafrom sensors 268 and 276.

Based on data collected in step 402, sub-controller 262 determines instep 404 the status of condenser 242 and condenser 243. If bothcondensers 242 and 243 are operating properly (i.e. status is OK), thenFlow Mode A (step 406) or Flow Mode B (step 408) is performed. In FlowMode A, all of working fluid 235 b from vessel 206 is directed throughfirst condenser 242. Therefore, valve 286 for second condenser 243 isclosed. In Flow Mode B, a flow of working fluid 235 b is splitessentially evenly such that approximately half of the volume of workingfluid 235 b flows through first condenser 242 and a second half ofworking fluid 235 b flows through second condenser 243.

A decision as to whether Flow Mode A or Flow Mode B is selected may beautomatically programmed into sub-controller 262. For example,sub-controller 262 may be programmed to remain at Flow Mode A for apredetermined time and periodically switch to Flow Mode B to alleviatesome of the load on Flow Mode A. Sub-controller 262 also may beconfigured such that the flow mode may automatically switch if any typeof problem is detected with either condenser 242 or 243. The flow modemay also be manually changed during operation of ORC system 200.

Returning to step 404, if sub-controller 262 determines that bothcondensers are not operating properly (i.e. status is not OK), then anext step in method 400 is to determine which condenser is not operatingproperly (step 410). If sub-controller 262 determines that firstcondenser 242 is problematic (step 412), then Flow Mode C is selected(step 414). In Flow Mode C, distribution of working fluid 235 b tosecond condenser 243 increases up to as high as 100% of the total flowof working fluid 235 b into pressure vessel 208. Depending on which modewas in operation prior to step 204, the flow percentage going intosecond condenser 243 may have previously ranged from zero percent toapproximately fifty percent of the total flow of working fluid 235 binto vessel 208. In Flow Mode C, an allocation of flow between firstcondenser 242 and second condenser 243 may depend on a furtherassessment of a condition of first condenser 242. In some cases, FlowMode C may automatically allocate all of working fluid 235 b throughsecond condenser 243. In that case, valve 284 would be completelyclosed.

Continuing with the steps in method 400, if it is instead determinedthat second condenser 243 is not operating properly (step 416), thenFlow Mode A is selected in step 418 such that all of working fluid 235 bis directed through first condenser 242, and valve 286 of secondcondenser 243 is closed.

If sub-controller 262 determines that neither first condenser 242 norsecond condenser 243 is operating properly (step 420), then it may benecessary to perform service on first and second condensers 242 and 243(step 422).

By having two condensers in pressure vessel 208, method 400 allows ORCsystem 200 to continue operating even when there is a problem with oneof condensers 242 or 243. As such, ORC system 200 is able to maintainits power rating over a longer period, compared to an ORC system whichwould normally have a reduction in power output when one of thecomponents is not operating at its maximum. Moreover, by making itfeasible to split flow through two condensers and/or switch flow to onecondenser as necessary, the load on each condenser 242 and 243 isreduced. As such, service problems may occur less often. If onecondenser is malfunctioning, operation of ORC system 200 may continueand the malfunctioning condenser may be serviced during a scheduledshutdown of ORC system 200.

It is recognized that sub-controller 262 may fluctuate between FlowModes A, B, and C based on predetermined parameters. Alternatively, asmentioned above, the flow modes may manually be switched.

The description of condensers 242 and 243 with reference to FIGS. 5 and6 is an example illustrating how the components of ORC system 200 ofFIG. 4 may operate and be controlled. It is recognized that the othercomponents (i.e. evaporators 232 and 233, turbines 238 and 239, andpumps 246 and 247) may be similarly designed with sensors and valves,such that the different flow modes described above for condensers 242and 243 may also apply to the other components.

FIG. 7 is another embodiment of an ORC system as an alternative to ORCsystem 100 of FIG. 3 and ORC system 200 of FIG. 4. Similar to system200, in ORC system 500, each of the main components of the ORC system(first evaporator 532, first turbine 538, first condenser 542, and firstpump 546) also includes a redundant component (second evaporator 533,second turbine 539, second condenser 543, and second pump 547). ORCsystem 500 also includes first power conditioner 550 and second powerconditioner 551. First and second evaporators 532 and 533 use geothermalheat source 536 (i.e. extracted oil) to vaporize working fluid 535;condensers 542 and 543 use sea water 531 to condense working fluid 535.

In the embodiment of FIG. 7, two controllers (first controller 548 andsecond controller 549) are shown in pressure vessel 512. Firstcontroller 548 may be designed as the main controller for ORC system 500and second controller 549 may be used during periods when firstcontroller 548 is not operating properly. Alternatively, secondcontroller 549 may be substituted periodically for first controller 548.As an alternative to the embodiment of FIG. 7, first and secondcontrollers 548 and 549 may be housed in separate pressure vessels.

As shown in FIG. 7, first evaporator 532 and second evaporator 533 arehoused in separate pressure vessels. Specifically, first evaporator 532is housed in vessel 504 and second evaporator 533 is housed in vessel505. An evaporator sub-controller is eliminated from this embodiment;instead, first and second evaporators 532 and 533 are controlled byfirst controller 548 (and second controller 549). Similarly, firstturbine 538 and first generator 540 are housed in pressure vessel 506;and second turbine 539 and second generator 541 are housed in pressurevessel 507. Turbines 538 and 539, and generators 540 and 541 may becontrolled by first controller 548 (and second controller 549).Similarly, power conditioners 550 and 551 may be controlled directly bycontrollers 548 and 549.

For evaporators 532 and 533, inlet streams of working fluid 535 a andheat source 536 are each split into two inlet streams (one for firstevaporator 532 and one for second evaporator 533) upstream of pressurevessels 532 and 533. In some embodiments, valves for controlling flowinto evaporators 532 and 533 may also be located in the piping upstreamof vessels 532 and 533.

First condenser 542 and second condenser 543 are both shown in pressurevessel 508. Also, sub controller 562 is shown inside pressure vessel508. It is recognized that first condensers 542 and 543 may beconfigured like evaporators 532 and 533 such that each is in its ownpressure and controlled by main controller 548, rather than asub-controller. The same applies for first pump 546 and second pump 547.

Various configurations of the embodiments shown in FIGS. 3, 4, 5, 5A and7 are possible. For example, some, but not all, of the main componentsof an ORC system (i.e. evaporator, turbine-generator, condenser andpump) may have a redundant component. For the components having a maincomponent and a redundant component, some of them may be housed in asingle pressure vessel, and some may be housed in separate pressurevessels. Some of the components may have a dedicated sub-controller,while others may be controlled by a main controller of the ORC system.

The embodiments described herein for a sub-sea ORC system offer numerousadvantages to a traditional ORC system housed in a single pressurevessel. Using pressure vessels for each of the components of the ORCsystem results in smaller pressure vessels that are easier to handle,and do not have the wall thickness requirements of a large pressurevessel. Moreover, by having the pressure vessels removably connected toone another, the ORC system makes it easier to substitute othercomponents as necessary. The use of redundant components (see FIGS. 4-7)allows the ORC system to continue operating even when one of the maincomponents of the ORC system is not operating properly. Morespecifically, the redundant component allows the ORC system to maintaina power rating even when the corresponding main component ismalfunctioning. In some embodiments in which a main component and aredundant component are housed in separate pressure vessels, service orroutine maintenance may be performed on one component without requiringany shutdown of the ORC system.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

1. An organic Rankine cycle (ORC) system for generating electrical power using a sub-sea geothermal source from a sea, the ORC system comprising: a first pressure vessel containing an evaporator configured to receive heat from the sub-sea geothermal source and vaporize an organic fluid passing through the first pressure vessel; a second pressure vessel removably connected to the first pressure vessel and containing a turbine configured to receive the organic fluid and expand the fluid to produce mechanical shaft energy convertible to electrical power; a third pressure vessel removably connected to the second pressure vessel and containing a condenser configured to condense the vaporized organic fluid flowing from the second pressure vessel and reject heat to cold sea water; and a fourth pressure vessel removably connected to the third pressure vessel and the first pressure vessel, and containing a pump configured to increase a pressure of the condensed organic fluid and recycle the organic fluid to the first pressure vessel.
 2. The ORC system of claim 1 wherein the pressure vessels are configured to be located on, near or below a sea floor.
 3. The ORC system of claim 1 further comprising: a fifth pressure vessel containing a controller configured to monitor and control operation of the evaporator, the turbine, the condenser and the pump.
 4. The ORC system of claim 3 further comprising: at least one redundant component selected from a group consisting of a second evaporator, a second turbine, a second condenser, and a second pump, wherein each redundant component is monitored and controlled by the controller.
 5. The ORC system of claim 4 wherein the controller directs at least a portion of the organic fluid through the at least one redundant component as a function of performance of at least one of the evaporator, the turbine, the condenser and the pump.
 6. The ORC system of claim 1 wherein the second pressure vessel further comprises a generator coupled to the turbine and configured to produce electrical energy.
 7. The ORC system of claim 6 further comprising: a power conditioner configured to condition the electrical energy from the generator into usable electrical power.
 8. The ORC system of claim 7 further comprising: a resistive bank configured to receive electrical power from the power conditioner in an absence of an electrical load.
 9. The ORC system of claim 1 wherein the first pressure vessel contains a heat exchanger connected to the evaporator, and the geothermal source passes through the heat exchanger to transfer heat to an intermediary fluid passing through the heat exchanger.
 10. A system for producing electrical power for sub-sea applications, the system comprising: a plurality of main components configured to operate as an organic Rankine cycle (ORC) system that generates electrical power using a working fluid that circulates through the main components; a plurality of pressure vessels removably connected to each other, wherein each pressure vessel contains a main component of the ORC system such that the working fluid circulates through each pressure vessel; a redundant component corresponding to one of the main components of the ORC system; and a control system to control operation of the main components and the redundant component, wherein operation of the redundant component includes at least one of maintaining the redundant component in a non-operational mode, operating the redundant component simultaneously with a corresponding main component, and operating the redundant component as a substitute to the corresponding main component.
 11. The system of claim 10 wherein the plurality of main components comprises: an evaporator configured to vaporize the working fluid; a turbine configured to receive the vaporized working fluid and expand the fluid to produce mechanical shaft energy convertible to electrical power; a condenser configured to condense the vaporized working fluid; and a pump configured to increase a pressure of the condensed working fluid and recycle the working fluid to the evaporator.
 12. The system of claim 11 further comprising a generator housed in the pressure vessel containing the turbine and coupled to the turbine to convert the shaft energy to electrical power.
 13. The system of claim 12 wherein the plurality of main components further comprises a power conditioner configured to condition the electrical power from the generator into a usable format, and the redundant component includes a second power conditioner.
 14. The system of claim 10 wherein the redundant component is housed in the pressure vessel containing the corresponding main component.
 15. The system of claim 10 wherein a main component of the ORC system is configured to receive a sub-sea geothermal source that passes through the main component and vaporizes the working fluid circulating through the ORC system.
 16. A method of generating electrical power for sub-sea applications using an organic Rankine cycle (ORC) system having each of an evaporator, a turbine, a condenser and a pump inside a separate pressure vessel to form a series of vessels removably connected to one another and configured to be placed proximate to a sea floor, the method comprising: circulating an organic fluid through the pressure vessels; generating mechanical shaft power using the organic fluid; and converting the mechanical shaft power to electrical power.
 17. The method of claim 16 further comprising: supplying heat from a sub-sea geothermal source to the evaporator to vaporize the organic fluid; and supplying cold sea water to the condenser to condense the organic fluid in the condenser.
 18. The method of claim 16 wherein the evaporator, the turbine, the condenser and the pump constitute main components of the ORC system, and the method further comprises: monitoring operation of the evaporator, the turbine, the condenser, and the pump; and flowing the organic fluid through at least one redundant ORC component selected from a group consisting of a second evaporator, a second turbine, a second condenser, and a second pump.
 19. The method of claim 18 wherein the at least one redundant ORC component is housed in the pressure vessel containing a corresponding main component.
 20. The method of claim 19 wherein the pressure vessel containing the main component and the at least one redundant component further includes a controller configured to control operation of the main component and the at least one redundant ORC component. 